Volume control construction



Feb. 11, 1947. JOHNSON VOLUME CONTROL CONSTRUCTION Filed Au 18, 1944Patented Feb. 11, 1947 VOLUME CONTROL CONSTRUCTION Esmond 'E. Johnson,Upper Darby, Pa., assignor to International Resistance Company,Philadelphia, Pa., a corporation of Delaware Application August 18,1944, Serial No. 550,111

3 Claims.

tical, simple and well able to withstand hard usage. Another object isto provide such a control which is particularly suited for use in radioequipment installed in conveyances, such as airplanes, where there ismarked vibration from engines or other sources. Another object is toprovide such a control in which any desired adjustment may be maintainedregardless of the shocks and vibrations the control may be subject to.Another object is to provide a control able to hold its adjustment underadverse conditions and which is wear-resistant so that it will givereliable operation over an extended period of time. Other objects willbe in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts as will beexemplified in the structure to be hereinafter described, and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the variouspossible embodiments of this invention: 7

. Figure 1 is a fragmentary elevation of a volume control having theinvention incorporated therein;

Figure 2 is a transverse sectional view taken along the line 2-2 ofFigure l;

Figure 3 is a fragmentary longitudinal section through the bushing andshaft of the volume control, the shaft being shown in elevation;

1 Figure 4 is a sectional view similar to Figure 2 before the shaft isinserted in the bushing; and

Figure 5 is a perspective of one of the parts of the volume control.

Similar reference characters refer to similar parts throughout theseveral views of the draw- As conducive to a clearer understanding ofcertain important features of this invention, it might here be pointedthat radio equipment now being built must be able to withstandsubstantial shocks as Well as continuous vibration. Such equipment isinstalled in various types of war vehicles, such as airplanes, boats,gun carriers, tanks, etc., where the engine vibration is considerableand where shocks may be heavy, particularly when in action. In suchapparatus it is vital to have the various adjustable parts, such as thevolume controls, hold adjusted positions. Many volume controls include aresistance strip which has a smooth surface and a brush arm or armaturein contact therewith. The brush arm moves about the resistance strip byrotation of the shaft. The friction between the brush and the strip isrelatively small. Consequently when subject to vibration, the brush isapt to move along the strip, and this results in a change of volumecontrol adjustment. Attempts to cure this difficulty include theprovision of some frictional element disposed between the end of theshaft and the inside of the casing. This element is usually formed fromsome composition such as rubber and is therefore subject to operativechange during use. Thus after a time, it may become useless, or at leastwill not prevent change of adjustment where there is heavy vibration.One of the objects of this invention is to provide a structure in whichthe above-mentioned difliculties are successfully overcome.

Referring now to Figure 1, there is shown a volume control of the usualconstruction and including a smooth resistance element and contactingbrush arm (not shown). The brush arm is rotated by a shaft Ill extendinginto a bushing II. The brush arm and the resistance element are enclosedwithin the casing I2, and suitable terminals generally indicated at I3extend from the casing.

Turning to Figure 3, the bushing II is undercut to provide an interiorportion Ila. extending from the bottom of the bushing, as viewed inFigure 1,v and terminating in a shoulder IIb formed by a smallerinterior portion IIc of the bushing. Accordingly, the shoulder IIb facesthe open end of the bushing or the bottom end as viewed in Figure 1.

As best seen in Figure 5, there is provided a cylindrical, frictionalelement I4 whose ends Ma and MD are spaced with a longitudinal openingtherebetween. A longitudinal projection M0 is stamped or otherwiseformed in the top of the frictional element, as viewed in Figure 5, i.e., opposite the space between the ends I41]. and Nb. Thus theprojection Me is convex to the inner surface of the element I4 andconcave to the outer surface thereof. The length of the element I4 isapproximately equal to the axial dimension of the enlarged portion Ila(Figure 3) of the bushing II, and element I4 is preferably formed from aresilient material such as spring steel or beryllium copper.

During assembly and before insertion of the shaft I and connected parts,the frictional element I4 is inserted in the enlarged portion Ha of thebushing to assume the position shown in Figures 2, 3, and 4. Thus theentire length of the element fits within enlarged portion Ha of thebushing and in transverse cross section the element which is larger indiameter than portion 1 la assumes the position shown in Figure 4. Dueto the larger diameter of the element 14 and the resilient characterthereof, the two sides of the element extending from the projection 14cpress firmly against the inner surface of the bushing. The parts in thisposition are so proportioned that the distance between the bottomsurface of the projection 4c (Figure 4) and a point on the linecontinuing the inner surface of the element directly therebeneath isshorter than the diameter of the shaft Ill.

Accordingly, upon insertion of the shaft I0 so that it is forced throughthe element M, the projection Mc flattens somewhat (Figure 2), It willbe understood that it is not necessary to assemble the parts in thissequence; the shaft can be inserted first, the element I4 being forcedin subsequently. When the shaft [0 presses and partially flattensprojection I40, it presses against the shaft, and the ends 14a and Mbare forced toward each other to press against this part of the shaft.Accordingly, the action of forcing the shaft intoassembled position notonly creates a pressure on the top of the shaft, as viewed in Figure 2,due to the flattening of the projection, but also on the bottom part ofthe shaft as the ends Ma and 1411 move toward each other.

*As assembled, the element I 4 is in position to press with considerableforce against the bushing I l and the shaft IA. The sides of the element44 are pressed firmly against the adjacent portions of the bushing dueto the pressure exerted by the shaft. At the same time the projectionI40 and the ends 14a and Mb press against the shaft as described above.Inasmuch as the control must be adjusted by rotation of the shaft whichmeans relative movement of the bushing H- and the shaft, there iscreated a considerable friction between these parts. This friction maybe varied to meet any desired specifications by a variation in the sizeof the parts as well as the resiliency of the frictional element. Thusthe friction may be such that it will not impede easy operation of thecontrol and yet will preventmovement of the shaft after an adjustment ismade in spite of any vibrations or shocks occurring during use of thecontrol.

Accordingly, the several objects hereinabove referred to have beensuccessfully accomplished and in a practical manner.

As many possible embodiments may be made of the above invention and asmany changes might be made in the embodiment above set forth, it is tobe understood that all matter hereinbefore set forth or shown in theaccompanying drawing is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In a volume control structure, in combination, a bushing having abore for the rotative support of a shaft, a shaft extendingtherethrough, said bore having an enlarged section, and a cylindrical,frictional element extending about said shaft within said enlargedportion of said bore in the bushing to press against said shaft and saidbushing, said element being split longitudinally and having alongitudinal ridge running parallel to the shaft axis and extendinginwardly opposite said split.

'2. In a volume control structure, in combination, a bushing, a shaftextending therethrough, and a cylindrical, frictional element extendingabout said shaft within said bushing to press against said bushing andsaid shaft, said element being split longitudinally and having alongitudinal ridge extending inwardly opposite said split, the distancebetween the inner surface of the ridge and a line continuing the innersurface of the element opposite thereto being smaller than the diameterof the shaft before insertion of the shaft.

3. In a volume control structure, in combination, a bushing including anundercut portion of enlarged diameter, a shaft extending therethrough,and a cylindrical clip fitting within said enlarged portion and havingcircumferentiallyspaced ends, the inner surface of said clip beingsmaller than the diameter of said shaft, there being a longitudinalprojection on said clip between the ends thereof to press against theshaft.

ESMOND E. JOHNSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,157,091 Baisch May 9, 1939784,272 Nagle Mar. 7, 1905 1,481,669 Justice Jan. 22, 1924 1,509,523Monosmith Sept. 23, 1924 1,588,039 Monosmith June 8, 1926 1,574,715Warner Feb. 23, 1926 1,780,172 Cramer Nov. 4, 1930 2,354,581 De J ongJuly 25, 1944 FOREIGN PATENTS Number Country Date 546,462 German Mar.19, 1932

